The olfactory and trigeminal nerves are often stimulated simultaneously by volatile chemical irritants. Odors are typically rich in quality, but the extent to which each of these neural inputs provides information about various attributes of the stimulus is unclear. Results of experiments conducted during the previous funding period suggest that activity in the trigeminal nerve provides little information about odor quality. This stands contrast to common experience: many attributes, e.g., sting, cool, burn, etc., have been associated with activation of the trigeminal nerve. To explore further the extent to which nasal- trigeminal information impacts on overall perception of odorants, we devise a method for measuring activation of the trigeminal nerve that takes advantage of the ability to determine which side of the nose is stimulated by an irritant (lateralization). We propose to measure, for the first time, lateralization thresholds for numerous odorants in individuals who have intact olfaction (normosmics) and those who have olfactory impairment (anosmic) to determine the relationship between activation of the olfactory system (threshold for odor detection) and the emergence of chemesthetic sensation (threshold for lateralization). Furthermore, we will examine the interactions between chemesthesis and olfaction during the perception of volatile chemicals. The results of these investigations will form the foundation upon which we will construct a new clinical test to assess the functional activation of the trigeminal nerve. After development and validation, we hope to incorporate this test into the battery of assessments that are performed on individuals who are referred to the Clinic for chemosensory evaluation.